We study the question of lower bounds for the Hausdorff dimension of a set in R n containing spheres of every radius. If n ≥ 3 then such a set must have dimension n. If n = 2 then it must have dimension at least 11/6. We also study the analogous maximal function problem and related problem of Besicovitch sets with an axis of symmetry.Besicovitch and Rado [1] and Kinney [5] proved the following result: There is a closed set E ⊂ R 2 with measure zero which contains a circle of every radius.The construction of Besicovitch and Rado works in R d : If d ≥ 3 there is a closed set E ⊂ R d with measure zero which contains a sphere of every radius. We will give an exposition of this construction in Section 1 below.One can ask whether a set containing a sphere of every radius must have Hausdorff dimension d. As it turns out, this question is easily answered in higher dimensions. In R 2 this may still be true but appears harder. One purpose of this paper is to prove the following partial result.Theorem 2. A Borel set in R 2 which contains a circle of every radius has Hausdorff dimension at least 11 6 . Following a known pattern (see [2] for example) we will derive Theorems 1 and 2 from L p → L q estimates for a related maximal function. Fix δ > 0.C δ (x, r) = {z ∈ R d : r − δ < |z − x| < r + δ}.